In response to membrane potential depolarization, voltage-dependent channels undergo a series of conformational changes from a non-conducting state (closed) to an activated (conducting), finally stabilizing in a non-conducting inactivated state. K+ channel function has been associated with such basic cellular functions as the regulation of electrical activity, signal transduction and osmotic balance. In higher organisms, K+ channel dysfunction may lead to uncontrolled periods of electrical hyperexcytability, like epileptic episodes, myotonia and cardiac arrhythmia. Consequently, efforts to understand K+ channel structure function and dynamics relate directly to human health and disease. The continuing long-term goal of this project is to further understand the molecular mechanisms of gating in voltage-dependent channels, by focusing on the analysis of K+ channel gating in prokaryotic and eukaryotic systems. Specifically we will address the following key questions: What are the atomic structures of the key conformations that determine channel activity? What are the molecular bases of gating in the 5s-to-ms regime? What is the mechanism of voltage sensing in voltage sensing domains? And how different parts of the channel interact to define open channel activity? We plan to study these problems by combining spectroscopic techniques (EPR and NMR), X-ray crystallography electrophysiological and computational methods. We intend to continue these structure-function studies by investigating proven model systems like the H+ activated channel from Streptomyces lividans and KvAP, the voltage-dependent channel from from Aeropyrum pernix, while extending them using new experimental approaches. In addition, we will focus our attention on the voltage sensing domain from the Ciona intestinalis-Voltage-Sensor-containing Phosphatase (Ci-VSP) and the hyperpolarization-activated six-transmembrane segment (6TM) channel from Methanococcus janschii (MVP). This proposal should open new experimental avenues that will contribute to our understanding of biologically important events such as electrical signaling, signal transduction and ion channel gating. PUBLIC HEALTH RELEVANCE: Understanding of K+ channel structure and function relates directly to health and disease, not only as key element in the most basic aspect of cellular function but due to its relationship to the mechanism of electrical excitability, cancer, and hormone secretion (diabetes) in humans. This is particularly relevant because of the known role of K+ channel dysfunction in a variety of pathological conditions. Some K+ channels are also involved as a virulence factor in prokaryotes and thus represent an important potential antibiotic target.